1. Field of the Invention
The present invention relates to an ink tank and a printing apparatus that can detect a residual quantity of ink in the ink tank, as well as a method of detecting the residual quantity of ink.
2. Description of the Related Art
Generally, as an ink supply source for various printing apparatuses including inkjet printing apparatuses, an ink tank of a cartridge type (hereinafter referred to as an ink cartridge) is adopted. Many ink cartridges that are detachable from respective printing apparatuses are known.
When ink in the ink cartridge is used up, a problem may occur in that a printing operation may be ceased halfway. In order to overcome this, there are proposed various mechanisms for detecting the ink residual quantity in the ink cartridge so that the ink or the ink cartridge may be replenished or replaced before the ink is used up and/or between printing operations. There are several mechanisms proposed as detection mechanisms for detecting the residual quantity of ink in the ink cartridge. For example, there is a mechanism for detecting the residual quantity of ink by checking a conduction state between electrodes provided in the ink cartridge. There is further a mechanism for detecting the residual quantity of ink by optical means, etc. Since means for detecting the existence or absence of the ink optically is simple in configuration and does not need a large device, it is employed in many ink cartridges.
As a mechanism for detecting the ink residual quantity optically, for example, Japanese Patent Laid-open No. H07-218321 (1995) proposes a mechanism using a prism. A detector mechanism for the ink residual quantity using the prism is equipped with a light-emitting part and a light-receiving part on the printing apparatus containing the ink cartridge, and is equipped with a prism reflecting surface that is constructed with a light transparent material, such as polypropylene, on or in the ink cartridge. When the ink in the ink cartridge is used up and an interface of the reflecting surface of the prism changes from polypropylene: ink to polypropylene: air, this causes a change of relative refractive index and the light from the light emitting part on the printing apparatus side undergoes total reflection on the reflecting surface of the prism, and is detected by the light receiving part on the printing apparatus side. The existence or absence of the ink in the ink cartridge is thus detected based on such a change of optical reflective intensity.
In the mechanism for detecting the existence and absence of the ink in the ink cartridge based on such a change of optical reflective intensity, there is a case where irregular reflection light and scattered light generated by the light from the light emitting part, in addition to the reflected light, may reach the light receiving part. The irregular reflection light and scattered light cannot always be discriminated from the reflected light coming from the prism, which can cause false detection of the existence or absence of the ink.
In order to overcome this, Japanese Patent Laid-open No. H10-323993 (1998) reports a method for detecting the existence and absence of the ink more accurately by providing a concave polyhedron in a prism basal plane part, and thereby reducing the reflected light in the prism basal plane part. Another method for detecting the existence and absence of the ink more accurately provides polarizing plates in front of the light-emitting part and the light-receiving part, and also means for changing an oscillating direction of the light immediately before the prism, and thereby reducing light other than the reflected light that is reflected at a boundary surface between the prism and the ink. However, with these methods, there is a risk that the reflected light reaching the light receiving part may decrease, thus rendering the result less robust.
Japanese Patent Laid-open No. 2006-159789 discloses a method for detecting the ink residual quantity based on light emitted by a luminescent material. Specifically, the ink contains the luminescent material. This method can solve a problem of the irregular reflection light and scattered light generated by the light from the light emitting part because the wavelength of the light emitted by the light emitting part and a wavelength of the light received by the light receiving part are different from each other. However, this method comes with a restriction that the luminescent material must be added into the ink.